Preparation And Performance Characterization Of Carbon Quantum Dots Fluorescent Spheres And Its Application In Immunochromatographic Test Strips

Lateral flow chromatography（LFA）technology has been widely used in the medical and environmental fields due to its advantages of rapidity,low cost,easy fabrication and detection,but the traditional LFA technology has the disadvantage of low sensitivity.The use of fluorescent materials as a signal for LFA technology has developed rapidly because it enables LFA technology with high sensitivity and multiplexing capabilities.Fluorescent nanocrystal-integrated spheres are the first choice for LFA technology signals,mainly because the fluorescent spheres are easy to operate and play a role in signal amplification.Fluorescent carbon dots（CDs）have great potential in the field of biosensing due to their unparalleled low toxicity and excellent water solubility.However,at present,the preparation of CDs-based fluorescent spheres is still challenging,which is mainly reflected in the following aspects:（i）High quantum yield.Only when the CDs-based fluorescent spheres have high quantum yield can the final immunodetection have high sensitivity;（ii）Uniform size.The size of CDs-based fluorescent spheres must be uniform to make the detection results reproducible;（iii）Fluorescence quenching.The aggregation-induced fluorescence quenching phenomenon of CDs is a major difficulty,and the prepared CDs-based fluorescent spheres must have solid-state fluorescence to achieve the application on LFA test strips;（iv）The stability of the binding of CDs to the carrier.Due to the small size of CDs and the complex functional groups on the surface,how to firmly anchor CDs on the carrier is another difficult problem.This paper aims to prepare CDs-based fluorescent spheres and further integrate them with LFA technology to achieve highly sensitive detection of various infectious diseases.The research of this paper is divided into the following four parts:（1）For the first time,CDs-based fluorescent spheres are used as the signal of LFA test strips.Blue fluorescent CDs/Si O₂ spheres（CSN）are obtained by co-hydrolysis of silanized CDs and TEOS by a template method.The uniformity of fluorescent sphere particle size is optimized by differential centrifugation.The LFA test strip with it as the signal substance is applied to detect SFTSV with high sensitivity.（2）Using template assembly to overcome the limitations in size and size distribution control of fluorescent spheres in system（1）.CDs-based Si O₂ spheres（FCS）are prepared by polymerizing blue fluorescent silanized CDs with dendritic Si O₂spheres through Si-O bonds,and the loading of CDs is optimized to maximize the fluorescence intensity of FCS.The LFA test strip with it as the signal substance was applied to detect Zi Ka with high sensitivity.（3）Red fluorescent is an important part of the panchromatic emission spectrum,and there is a large exploration space for preparing of high-performance CDs-based red fluorescent spheres.In this part of the study,the amino group at the long-chain end of the silanizing agent（N-β-（Aminoethyl）-γ-aminopropyltrimethoxysilane（AEAPTMS））is used to anchor the red fluorescent CDs and enhance their luminescence intensity,and the siloxane group at the other end was hydrolyzed to silanol and grafted to the inner wall of the dendritic silica sphere.Thus,red fluorescent CDs are assembled into dendritic silica spheres to prepare CDs-based red fluorescent spheres（RCS）.The synthesis mechanism and related luminescence mechanism of the fluorescent sphere were expounded,and it was used as the signal substance of LFA technology for highly sensitive detection of COVID-19.（4）In situ synthesis of CDs in pre-synthesized spheres can avoid the obstacles of purification/extraction and surface modification of CDs faced by CDs to prepare fluorescent spheres.In this research section,in situ synthesis of fluorescent CDs on Si O₂ spheres（CSS）by one-step hydrothermal treatment of trisodium citrate and AEAPTMS grafted dendritic Si O₂.Through optimization,the relative quantum yield of blue fluorescence from a single-emission CSS aqueous solution can be as high as 89.3%.As the hydrothermal reaction time increases,the CSS aqueous solution exhibits additional green fluorescence with dual emission characteristics,and still has a high relative quantum yield.Changes in the fluorescent properties of CSS are explained and validated.The best-performing CSS was used as the signal of LFA technology for highly sensitive detection of anthrax.In summary,in this paper,four different types of CDs-based fluorescent spheres are prepared by using silica as the carrier in four ways.The integration of CDs in silica spheres can amplify the signal for the detection of LFA,and the fluorescent CDs-based nanospheres are simple to operate and easy to biofunctionalize.In addition,the CDs are localized into the silica matrix resulting in strong stability of the fluorescent CDs-based silica spheres.Based on four different CDs-based fluorescent spheres with high quantum yield,four types of LFA test strips have been successfully constructed to achieve highly sensitive point-of-care detection of various infectious diseases.